It is well known that the fullness of tone of an instrument, an orchestra or a choir depends upon the number of individual sound elements or voices that are heard at the same time. Thus, for example, ten violins simultaneously playing one and the same note provide a richer tone than one violin which is raised to the same sound level as the ten violins by means of an electro-acoustic amplifying system. The same naturally applies in the case of instruments that are able to emit simultaneously a plurality of sound elements or voices of the same note; a particular example of such an instrument is the organ.
In the building of electronic organs two concepts have been employed, namely that of the synchronous organ and that of the asynchronous organ. All tones of the synchronous organ are produced from twelve master voices corresponding to the twelve semi-tones of the tempered scale. This is effected by division or multiplication of frequency. By reason of exact mathematicl dependence of the tones of a register on their particular master voices, all the octave tones are simultaneously identical with the harmonics of the basic tone; this means that, as regards fullness of tone, the entire instrument emits a sound like a register rich in overtones. Unfortunately, it is not possible to increase the richness of tone beyond this. The synchronous organ however offers the considerable advantage of low cost and great pitch constancy.
In the case of the asynchronous organ, however, the individual voices are produced in individual tone generators equivalent to organ pipes. The fullness of tone of organs of this kind can be increased as required by increasing the number of individual generators and by their multiple use. This method is complicated and therefore very costly; furthermore, the cost and difficulty involved in maintenance can be considerably greater for asynchronous organs, particularly in view of the large number of individual tone generators (e.g. 500 as compared with 12 in the case of the synchronous organ).
It is an aim of the invention to provide a method and apparatus in which the fullness of tone of such musical instruments can be increased without the use of complicated, and therefore expensive, equipment.